National Conferences Articles

We present a novel analytical method for the evaluation of the Bit-Error-Probability (BEP) of optically pre-amplified Pulse-Position-Modulation (PPM) receivers. The method takes into account the non-ideal optical filter response and utilizes a finite series expansion to calculate the BEP. Using the proposed approach, it is possible to accurately evaluate the PPM BEP for arbitrarily shaped filters where the well-established χ2 method only provides approximate results. The method is applied for ideal passband and Lorentzian response wide optical filters, and the obtained results are in perfect agreement with the χ2 approximation for the ideal filter, while a discrepancy of 0.5 dB is observed between the two methods for the Lorentzian filter.

Swarms of cooperative Unmanned Aerial Vehicles (UAVs) have emerged as a new promising solution for accomplishing complex and large scale tasks, that would be challenging or even impossible for a single UAV. Coordinating multiple UAVs towards a common mission is quite challenging, as multiple operational factors must be ensured in terms of flight reliability, safety, resource allocation and ubiquitous communications. This paper presents an integrated UAV swarm management platform for autonomous area and infrastructure inspection and proposes a novel network architecture for relaying swarm communications in underserved areas. Real trials and measurements were performed on the field, providing preliminary results and proof-of-concept insights.

The fifth generation (5G) mobile networks have adapted new features compared to the previous generation that resulted in increased overall throughput and decreased latency. At the same time the complexity of 5G-based standards and deployment scenarios has increased. The new features of the physical layer gather interest not only in the development of software, but also in the field of measurements and performance evaluation, among the research community. This paper proposes a flexible End-to-End (E2E) standalone 5G system platform that can be fully reprogrammable and customizable to serve as a basis for research that can be expanded to all aspects of a 5G system design. The main capabilities and use cases of the platform are presented and conclusions are made based on the conducted tests and measurements.

In this paper, we evaluate the performance of a vehicular ad hoc network that enables Vehicle-to-Everything (V2X) communication considering direct and indirect packet transmission. As a performance indicator, we use the blocking probability due to the unavailability of resources. For the blocking probability calculation, we utilize two loss models from the teletraffic theory. The results demonstrate that both the capacity of the V2X links and the number of hops in the multi-hop transmission significantly affect the blocking probability of a request for service and consequently the QoS.

We present results for the performance of a preamplified optical receiver using LDPC and RS error correction codes. The LDPC codes under consideration were recently proposed for the 5G communication standard and their construction is suitable for correcting the burst errors that are introduced by PPM. The results show that the LDPCs can provide a very significant coding gain in comparison with the uncoded system. They also perform better than RS codes of an equal code rate and equivalent data block size.

Reliable and ubiquitous communications, offering high data rates, low latency and supporting large numbers of connected devices, are critical requirements for modern emergency rescue missions. Multiple teams of First Responders, operating at remote areas, on rough terrain or under harsh conditions (e.g. wildfires, earthquakes, flooding etc.) need seamless connectivity to send/receive mission data and organize their operations. This paper, based on the communication platform of RESPOND-A project for supporting First Responders' missions, proposes a communication relay architecture for extending the 5G network, covering network gaps or underserved areas, while still supporting the mission requirements. Preliminary field measurements were also taken for providing a proof-of-concept and evaluating the systems' performance.

Τhis paper focuses on the latest trends on software defined radio platforms based on open source software and aims to highlight the benefits that these platforms offer in terms of flexibility and cost. The requirements of hardware and the special features of operating systems that enable the SDR software to run on x86-64 systems are presented in detail. Moreover an emphasis is given to the software architectures used in open source projects implementing wireless protocols. As a paradigm of an open source SDR platform we emulate a 5G system, based on Open Air Interface software and docker engine, installed on a Linux PC. Finally, the main aspects of this emulation are presented and conclusions are made.

In this paper we study the downlink of an Orthogonal Frequency Division Multiplexing (OFDM) based cell that accommodates calls from different service-classes with different resource requirements. We assume that calls arrive in the system according to a Poisson process while the call admission is based on restricted accessibility. In a restricted accessibility system, a new call may be blocked even if available resources do exist at the time of its arrival. To determine, via recursive formulas, the most important performance metrics, i.e., Call Blocking Probabilities (CBP) and resource utilization in this system, we model the system as a multirate loss model. The accuracy of the proposed formulas is verified via simulation and found to be quite satisfactory.

The presence of software and middleware technologies based on open APIs and protocols for advanced service provision in telecoms is the main subject of this article. Specifically, the role and the trade-off between open APIs and Protocols, i.e. OSA/Parlay APIs, JAIN APIs and SIP, in modern telecoms are addressed. We present a technical implementation analysis, based on a call-related telecom service, in order to set a common basis for the aforementioned technologies, since - either way - "voice" is still a common denominator for Fixed and Mobile Operators as well as for Internet Service Providers too. We summarize with a performance evaluation study regarding the implemented services.

In this paper, a study on the end-to-end performance of multihop non-regenerative relaying over independent and identical generalized-gamma fading channels is presented. Novel closed-form bounds for the cumulative distribution function, the moments, and the moment generating function (MGF) of the end-to-end signal-to-noise ratio are presented. Using the MGF-based approach, closed-form expressions for the amount-of-fading, the outage probability, and the average bit error probability for binary differential phase shift keying are derived. In order to validate the accuracy of the proposed mathematical analysis, various numerical and computer simulation results are presented and compared to the analytical ones.